Method for passivating metallic surfaces by using itaconic acid homopolymers or copolymers

ABSTRACT

A process for passivating a metallic surface by treating it with an acidic aqueous preparation comprising at least one itaconic acid homo- or copolymer. Passivating layers and metallic surfaces obtainable by means of the process.

The present invention relates to a process for passivating metallicsurfaces by treating them with an acidic, aqueous preparation whichcomprises at least one homopolymer or copolymer of itaconic acid. Theinvention further relates to passivating layers and to metallic surfaceswhich are obtainable by means of the process.

The corrosion protection treatment of modern metallic materials normallytakes place in multistage operations, and the surface of treated metalsnormally has a number of different layers.

The protection of metallic components against corrosion is of greateconomic importance. At the same time the requirements imposed on thecorrosion protection are also becoming ever more stringent. An exampleof this is that the newer models of automobile are nowadays warrantedwith a guarantee of up to 12 years against rust perforation.

Of particular importance both technically and economically is thecorrosion protection treatment of aluminum surfaces and also of thesurfaces of galvanized metals, especially electrochemically galvanizedor hot-dip-galvanized iron and steel. The corrosion protection affordedby the zinc is based on the fact that it is baser than the metallicmaterial itself and therefore to start with undergoes corrosion itself.The metallic material itself remains intact as long as it is stillcovered by a continuous layer of zinc.

In the presence of atmospheric oxygen a thin oxide layer forms initiallyon the surface of Zn or Zn alloys, Al or Al alloys and slows thecorrosive attack on the underlying metal to a greater or lesser degreedepending on the external conditions.

In order to strengthen the protective effect of such an oxide layer,surfaces of Al and Zn are regularly subjected to an additionalpassivating treatment. In the course of such treatment a fraction of themetal to be protected dissolves and is immediately reincorporated intoan oxide film on the metal surface. This film is similar to the oxidefilm which is present in any case, but it offers greater protection. Itis normally referred to as a passivating layer. In many cases it alsoimproves the adhesion of paint layers applied to the metal. Instead ofthe term “passivating layer”, therefore, the term “conversion coat” isoften used synonymously, and sometimes also the term “pretreatmentlayer” or “posttreatment layer”, depending on the point in theproduction process at which the treatment takes place. Passivatinglayers are comparatively thin and normally have a thickness of not morethan 3 μm.

In order to reinforce the corrosion protection it is common to applyadditional (paint) layers to the passivating layer. Such systems usuallycomprise a combination of two or more paint layers each of which servedifferent purposes. They serve to protect the passivating layer and themetal against corrosive gases and/or liquids and also against mechanicaldamage, such as stone chipping, for example, and of course also serveesthetic purposes. Paint layers are normally much thicker thanpassivating layers. Typical thicknesses range from 5 μm to 400 μm.

The passivation can be employed for permanent corrosion protection orelse only for temporary corrosion protection. Temporary protection isused only for the storage or transportation of a metal sheet or othermetallic workpiece and is removed again before final processing.

Passivating layers on zinc or aluminum surfaces have generally beenobtained to date by treating the workpiece requiring protection withacidic aqueous solutions of CrO₃. The mechanism of such passivation iscomplex. It includes the dissolution of metallic Zn or Al from thesurface and its reprecipitation in the form of amorphous zinc-chromiumoxides or aluminum-chromium oxides, respectively. The layers may,however, also comprise extraneous ions and/or further components fromthe treatment solution. In the case of treatment with chromic acid inparticular it is impossible to rule out the incorporation into thepassivating layer of a certain fraction of Cr(VI).

In order to avoid treatment with carcinogenic Cr(VI) solutions proposalshave been made to carry out treatment of metallic surfaces with acidic,aqueous Cr(III) solutions. By way of example reference may be made toU.S. Pat. No. 4,384,902 or WO/40208. Increasingly, however, there arecustomers on the market who require completely chromium-free processesfor passivating, In order to avoid the use of Cr(VI) and Cr(III),therefore, the use of polymers is increasingly gaining in importance.

DE-A 195 16 765 discloses a chromium-free and fluoride-free process forproducing conversion coats of metallic surfaces of Zn or Al. The acidicsolution used for passivation comprises a water-soluble polymer,phosphoric acid, and Al chelate complexes. As an option it is alsopossible to use polymers and copolymers of (meth)acrylic acid.

DE-A 197 54 108 discloses a chromium-free aqueous corrosion protectioncomposition which comprises hexafluoro anions of Ti(IV) and/or Zr(IV),vanadium ions, cobalt ions, and phosphoric acid. As an option it is alsopossible for various film-forming polymers to be added as well,including carboxyl-containing copolymers such as acrylic acid/maleicacid copolymers.

JP-A 2001-164377 discloses the production of black steel sheets for theproduction, for example, of black casings for consumer electronics. Themetal sheet is coated with a paint comprising metal ions, awater-soluble polymer, an aqueous polymer dispersion, and an acid. Oneexample mentions a water-soluble polymer of 70% acrylic acid and 30%itaconic acid. The passivation of metals by means of an itaconic acidcopolymer is not disclosed by the document.

JP-A 2001-158969 discloses a final coating for metallic surfaces,particularly of said black casings, with 50% to 98% by weight of anaqueous polymer dispersion, metal ions, a water-soluble polymer, and anacid. One example mentions a water-soluble polymer of 70% acrylic acidand 30% itaconic acid. The passivation of metals by means of an itaconicacid copolymer is not disclosed by the document.

JP-A 2003-027202 discloses a process for treating a galvanized steelsheet with a composition composed of a metallic compound, awater-soluble organic resin, and an acid. The polymer may comprise,among others, a copolymer formed from a carboxyl-containing monomer andalso further carboxyl-containing monomers or OH-containing monomers. Theexamples mention a copolymer of 70% acrylic acid and 30% itaconic acid.The document contains no indications of how the polymer is prepared.

Our as yet unpublished application DE 103 53 845, unpublished at thepriority date of the present specification, discloses a process forpassivating metal surfaces using copolymers of 50% to 99.9% by weight(meth)acrylic acid, 0.1% to 50% by weight acidic comonomers, includingethylenically unsaturated dicarboxylic acids, and, optionally, 0% to 30%by weight further comonomers. The dicarboxylic acid may for example beitaconic acid. The document, however, contains no indications ofparticular preparation processes for itaconic acid polymers.

As well as achieving very good corrosion protection, a process forpassivating, particularly a chromium-free process, is also required tomeet a series of technical requirements.

The passivation can be performed by immersing the workpieces requiringpassivation in a passivating solution. Loose workpieces (screws, forexample) can be placed in a drum for this purpose, and the drumimmersed. Larger workpieces can also be mounted on a suitable frame, andthe frame immersed. With the dipping method the skilled worker iscomparatively free to determine the contact time between the passivatingsolution and the workpiece, and hence even quite thick passivatinglayers can be obtained. The contact time may well be of the order ofminutes. Where this technique is employed, more complex workpieces areusually assembled first—welded together from steel parts, forexample—and then galvanized and passivated as a whole.

For producing sheetlike metallic workpieces such as automobile parts,bodywork parts, instrument casings, façade cladding, ceiling panels orwindow profiles, for example, metal sheets are shaped by means ofsuitable techniques such as punching, drilling, folding, profilingand/or deep drawing. Larger components, such as automobile bodies, forexample, are assembled if appropriate by welding together a number ofindividual parts. The raw material for this purpose normally compriseslong metal strips, which are produced by rolling the metal and which forthe purposes of storage and transportation are wound up to form what arecalled coils.

The galvanizing and passivation of such metal strips is carried outindustrially in continuous plants. For galvanizing, first of all, themetal strip is run through a galvanizing apparatus, such as a trough ofmolten zinc, for example, and then through a further, passivatingapparatus, again a trough, for example, or a rinsing apparatus. As ageneral rule, further process steps are carried out continuously:cleaning or rinsing steps, for example, or else the application of afirst paint layer to the passivating layer. Typical speeds at whichmetal strips are run through the continuous plants are 50 to 100 m/min.This means that the contact time between the metallic surface and thepreparation used for passivating is short. Normally only a few secondsare available for the treatment. A process suitable industrially musttherefore provide adequate results even with only short contact times.

It was therefore an object of the invention to provide an improved,preferably chromium-free process for passivating metallic surfaces ofZn, Zn alloys, Al or Al alloys which affords improved corrosionprotection as compared with the prior art and in which only shortcontact times between the metallic surface and the preparation used forpassivating are required in order to achieve a result which isnevertheless satisfactory. In particular it ought also to be possible toimplement the process continuously.

The invention accordingly provides a process for passivating a metallicsurface, in which said surface is treated with an acidic, aqueouspreparation comprising at least one water-soluble itaconic acid homo- orcopolymer, the polymer having been constructed from the followingmonomeric units:

-   (A) 0.1% to 100% by weight of itaconic acid,-   (B) 0% to 99.9% by weight of at least one monoethylenically    unsaturated monocarboxylic acid, and-   (C) 0% to 40% by weight of at least one further ethylenically    unsaturated monomer, other than (A) and (B), which contains acid    groups,    -   and/or-   (D) 0% to 30% by weight of at least one further ethylenically    unsaturated monomer, other than (A), (B) and (C),    -   the amount being based in each case on the total amount of all        of the monomers incorporated in the copolymer,        where the copolymer is obtainable by means of free-radical        polymerization in aqueous solution at a temperature of less than        120° C.

In one preferred embodiment of the invention the metallic surface is thesurface of a strip metal and with further preference the passivation isperformed by means of a continuous process.

The invention further provides a passivating layer on a metallicsurface, which is obtainable by means of the process, and also providesmetallic surfaces comprising such a passivating layer.

Surprisingly it has been found that the metal surfaces obtained by meansof the process of the invention using itaconic acid polymers aresignificantly more resistant to corrosion than when using knownpolymers, such as acrylic acid-maleic acid copolymers, for example.Surprisingly in particular, the itaconic acid copolymers synthesizedinventively at less than 120° C. exhibit a much better corrosionprotection effect than itaconic acid copolymers which have beensynthesized at higher temperatures.

The acrylic acid-itaconic acid copolymers prepared in accordance withthe invention result in a significantly improved passivation incomparison to acrylic acid-maleic acid copolymers. The itaconic acidcopolymers have lower residual monomer contents than correspondingmaleic acid copolymers. By substituting itaconic acid for maleic acid itis possible to obtain a higher dicarboxylic acid fraction in thepolymers of the invention, which is likewise beneficial to thepassivating properties.

Details of the invention now follow:

The metallic surfaces which can be passivated by means of the process ofthe invention comprise, in particular, the surfaces of base metals. Thesurface in question may be, for example, that of iron, steel, Zn, Znalloys, Al or Al alloys.

The process of the invention is particularly suitable for passivatingmetallic surfaces of Zn, Zn alloys, Al or Al alloys. These may be thesurfaces of structures or workpieces composed entirely of said metals oralloys. Alternatively they may be the surfaces of structures coated withZn, Zn alloys, Al or Al alloys, it being possible for the structures tobe composed of other materials: other metals, alloys, polymers orcomposites, for example. The surface in question may in particular bethat of galvanized iron or steel. In one particular embodiment of theprocess it is the surface of a strip metal, in particularelectrolytically galvanized or hot-dip-galvanized steel.

Zn alloys or Al alloys are known to the skilled worker. The skilledworker selects the type and amount of alloying constituents inaccordance with the desired end application. Typical constituents ofzinc alloys for hot-dip processes comprise, in particular, Al, Pb, Si,Mg, Sn, Cu or Cd. Zinc alloys which are deposited electrolyticallytypically comprise Fe, Co, Ni or Mn. Method comprise Typicalconstituents of aluminum alloys comprise, in particular, Mg, Mn, Si, Zn,Cr, Zr, Cu or Ti. The alloys in question can also be Al/Zn alloys, inwhich Al and Zn are present in approximately equal amounts. Steel coatedwith such alloys is available commercially.

The preparation used for passivating comprises one or more homopolymersand/or copolymers comprising itaconic acid units and also, ifappropriate, monoethylenically unsaturated monocarboxylic acids andalso, optionally, further monomers as structural units.

The polymers used are water-soluble or at least water-dispersible. Theterm “water-soluble” for the purposes of this invention is intended todenote that the copolymer or copolymers used should be homogeneouslywater-soluble. The term “water-dispersible” means that, although thesolution is not completely clear, the polymer is distributedhomogeneously therein and also does not settle. Preference is given topolymers which are water-soluble.

The copolymers used ought preferably to be infinitely miscible withwater, even if this is not absolutely necessary in every case. Theymust, however, be water-soluble at least to an extent such thatpassivation by means of the process of the invention is possible.

As a general rule the copolymers used ought to have a solubility of atleast 50 g/l, preferably 100 g/l and more preferably at least 200 g/l.

The skilled worker in the field of water-soluble polymers is aware thatthe solubility of COOH-containing polymers in water may be dependent onthe pH. The reference point chosen should therefore in each case be thepH which is desired for the particular end use. A copolymer which at onepH has a solubility which is inadequate for the intended use may have anadequate solubility at a different pH.

The monomer (A) for preparing the homopolymer or copolymer used inaccordance with the invention is itaconic acid:

The itaconic acid may also be used in the form of its salts: forexample, as an alkali metal salt or ammonium salt. Additionally it isalso possible to use derivatives of itaconic acid which readilyhydrolyze to itaconic acid in aqueous solution, such as, for example,the corresponding anhydride, monoesters or diesters or acid amides. Itwill be appreciated that mixtures of such derivatives can also be used.

The polymer used in accordance with the invention may be a homopolymeror, preferably, a copolymer of itaconic acid.

The amount of itaconic acid in the polymers is 0.1% to 100% by weight,preferably 10% to 50% by weight, more preferably 15% to 45% by weight,very preferably 20% to 40% by weight and, for example, 25% to 35% byweight, this figure being based on the sum of all of the monomers in thepolymer.

The polymer used in accordance with the invention may further compriseup to 99.9% by weight of one or more monomers (B). These aremonoethylenically unsaturated monocarboxylic acids.

Examples of suitable monoethylenically unsaturated monocarboxylic acids(B) comprise acrylic acid, methacrylic acid, crotonic acid, vinylaceticacid or else C₁-C₄ monoesters of monoethylenically unsaturateddicarboxylic acids. Preferred monomers are acrylic acid and methacrylicacid, particular preference being given to acrylic acid.

It will be appreciated that mixtures of two or more differentmonoethylenically unsaturated monocarboxylic acids can also be used.

The amount of all monomers (B) together is preferably 50% to 90% byweight, more preferably 55% to 85% by weight, very preferably 60% to 80%by weight, and, for example, 65% to 75% by weight.

Optionally the copolymer of the invention may further include 0% to 40%by weight of at least one further ethylenically unsaturated monomer (C),different from (A) and (B).

The monomers (C) have in each case at least one acidic group. Withparticular preference they are in each case monoethylenic monomers. Themonomers (C) are free-radically polymerizable.

The monomers (C) may be, for example, carboxyl-containing monomers (C1),monomers (C2) comprising phosphoric acid groups and/or phosphonic acidgroups, or monomers (C3) comprising sulfonic acid groups.

The monomers (C) can also be used in the form of their salts: forexample, as alkali metal salts or ammonium salts. Additionally it isalso possible to use derivatives of the monomers (C) which readilyhydrolyze to the free acids in aqueous solution, such as anhydrides,monoesters or diesters or acid amides, for example. It will beappreciated that mixtures of such derivatives can also be used.

Examples of carboxyl-containing monomers (C1) comprise, in particular,ethylenically unsaturated dicarboxylic acids such as maleic acid,mesaconic acid, citraconic acid, fumaric acid or methylenemalonic acid.A preferred monomer (C1) is maleic acid and/or maleic anhydride.

Examples of suitable monomers (C2) comprise vinylphosphonic acid,monovinyl phosphate, allylphosphonic acid, monoallyl phosphate,3-butenylphosphonic acid, mono-3-butenyl phosphate,mono(4-vinyloxybutyl) phosphate, phosphonoxyethyl acrylate,phosphonoxyethyl methacrylate, mono(2-hydroxy-3-vinyloxypropyl)phosphate, mono(1-phosphonoxymethyl-2-vinyloxyethyl) phosphate,mono(3-allyloxy-2-hydroxypropyl) phosphate,mono(2-allyloxy-1-phosphonoxymethylethyl) phosphate,2-hydroxy-4-vinyloxymethyl-1,3,2-dioxaphosphole, and2-hydroxy-4-allyloxymethyl-1,3,2-dioxaphosphole. It is also possible touse salts and/or esters, especially C₁ to C₈ monoalkyl, dialkyl and, ifappropriate, trialkyl esters, of the monomers containing phosphoric acidand/or phosphonic acid groups.

One preferred monomer (C2) is vinylphosphonic acid, or hydrolyzableesters thereof.

Examples of monomers (C3) containing sulfonic acid groups compriseallylsulfonic acid, methallylsulfonic acid, styrenesulfonate,vinylsulfonic acid, allyloxybenzenesulfonic acid or2-acrylamido-2-methylpropanesulfonic acid, 2-(methacyloyl)ethylsulfonicacid and the alkali metal salts thereof.

It will be appreciated that mixtures of two or more different monomers(C) can also be used. Preference is given to monomers (C1) comprisingcarboxyl groups and also to monomers (C2) comprising phosphoric acidgroups and/or phosphonic acid groups.

If monomers (C) are present their amount together is preferably 0.1% to20% by weight, more preferably 0.2% to 15% by weight, and verypreferably 0.5% to 10% by weight.

If monomer (C) comprises monomers comprising phosphoric acid groupsand/or phosphonic acid groups, and particularly vinylphosphonic acid,amounts of 5% to 40% by weight, preferably 10% to 30% by weight, morepreferably 12% to 28% by weight, and very preferably 20% to 25% byweight have proven appropriate.

Furthermore, optionally, the copolymer may comprise 0% to 30% by weightof at least one further free-radically polymerizable, ethylenicallyunsaturated monomer (D), different from (A), (B) and (C). Over and abovethis no further monomers are used. The monomers (D) serve to fine-tunethe properties of the copolymer. They are selected by the skilled workerin accordance with the desired properties of the copolymer. The monomers(D) are likewise free-radically polymerizable.

Preferably they are likewise monoethylenically unsaturated monomers. Inparticular cases, however, it is also possible to use small amounts ofmonomers having two or more polymerizable groups. This allows thecopolymer to be crosslinked to a slight extent.

Examples of monomers (D) comprise C₁ to C₈ alkyl esters or C₁ to C₄hydroxyalkyl esters of (meth)acrylic acid, such as methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate or butane-1,4-diol monoacrylate. The alcohol componentsin the (meth)acrylic esters may also be alkoxylated alcohols. Mentionmay be made here in particular of alkoxylated C₁ to C₁₈ alcohols whichhave 2 to 80 mol of ethylene oxide, propylene oxide, butylene oxide ormixtures thereof. Examples of such alkoxylated products comprise methylpolyglycol (meth)acrylate or (meth)acrylic esters of C₁₃/C₁₅ oxo alcoholreacted with 3, 5, 7, 10 or 30 mol of ethylene oxide, and/or mixturesthereof, (methyl)styrene, maleimide, N-alkylmaleimide, maleic acidmonoamides or maleic monoesters.

Also suitable are vinyl or allyl ethers such as, for example, methylvinyl ether, ethyl vinyl ether, propyl vinyl ether, isobutyl vinylether, 2-ethylhexyl vinyl ether, vinyl cyclohexyl ether, vinyl4-hydroxybutyl ether, decyl vinyl ether, dodecyl vinyl ether, octadecylvinyl ether, 2-(diethylamino)ethyl vinyl ether, 2-(di-n-butylamino)ethylvinyl ether or methyldiglycol vinyl ether, and the corresponding allylcompounds. Use may likewise be made of vinyl esters such as vinylacetate or vinyl propionate, for example.

Examples of basic monomers comprise acrylamides and alkyl-substitutedacrylamides, such as acrylamide, methacrylamide, N-tert-butylacrylamideor N-methyl(meth)acrylamide. Additionally it is also possible to usebasic monomers such as 1-vinylimidazole and N-vinylpyrrolidone.

Examples of crosslinking monomers comprise molecules having two or moreethylenically unsaturated groups, examples being di(meth)acrylates, suchas ethylene glycol di(meth)acrylate or butane-1,4-diol di(meth)acrylateor poly(meth)acrylates such as trimethylolpropane tri(meth)acrylate orelse di(meth)acrylates of oligoalkylene or polyalkylene glycols, such asdi-, tri- or tetraethylene glycol di(meth)acrylate. Further examplescomprise vinyl (meth)acrylate or butanediol divinyl ether.

It will be appreciated that a mixture of different monomers (D) can alsobe used. The amount of all monomers (D) used together is 0% to 30% byweight, based on the total amount of all of the monomers used for theprocess. Preferably, the amount is 0% to 20% by weight, more preferably0% to 15% by weight, and very preferably 0% to 10% by weight. Ifcrosslinking monomers (D) are present their amount should generally notexceed 5%, preferably 2% by weight, based on the total amount of all ofthe monomers used for the process. The amount can be, for example, 10ppm to 1% by weight.

The skilled worker chooses the nature and amount of the monomers used inaccordance with the desired passivation. In doing so, he or she willtake account of the fact that the polymer is to be water-soluble orwater-dispersible. Monomers which might impair the water-solubility ofthe polymer are therefore used by the skilled worker only in amountssuch that no adverse effects can occur.

Particular preference is given to copolymers of about 25% to 30% byweight itaconic acid and about 70% to 75% by weight acrylic acid, inparticular about 26% to 28% by weight itaconic acid and about 72% to 74%by weight acrylic acid.

Particular preference is given, moreover, to terpolymers of about 23% to30% by weight itaconic acid, about 67% to 75% by weight acrylic acid andabout 0.1% to 10% by weight vinylphosphonic acid, in particular about25% to 27% by weight itaconic acid, about 68% to 70% by weight acrylicacid and about 3% to 5% by weight vinylphosphonic acid.

In a further embodiment of the invention terpolymers of about 10% to 30%by weight itaconic acid, about 50% to 70% by weight acrylic acid, andabout 10% to 30% by weight vinylphosphonic acid, in particular about 15%to 25% by weight itaconic acid, about 55% to 65% by weight acrylic acid,and about 15% to 25% by weight vinylphosphonic acid, have provenappropriate.

The monomers used are polymerized free-radically in aqueous solution.

The term “aqueous” means that the solvent or diluent used has water asits main constituent. Besides water, however, there may also befractions of water-miscible organic solvents. This may be necessary, forexample, in order to improve the solubility of certain monomers,particularly the monomers (D), in the reaction medium.

The solvent or diluent used accordingly contains at least 50% by weightof water relative to the total amount of the solvent. Besides this theremay be one or more water-miscible solvents used. Mention may be madehere in particular of alcohols, examples being monoalcohols such asethanol, propanol or isopropanol, dialcohols such as glycol, diethyleneglycol or polyalkylene glycols, or derivatives thereof. Preferredalcohols are propanol and isopropanol. The water fraction is preferablyat least 70%, more preferably at least 80% and very preferably at least90% by weight. With very particular preference water exclusively isused.

The conduct of the free-radical addition polymerization is known inprinciple to the skilled worker.

The free-radical addition polymerization is preferably initiated byusing suitable polymerization initiators. Alternatively, however, it canalso be triggered by means, for example, of appropriate radiation. Thefree-radical initiators ought to be soluble in the reaction solvent,preferably water-soluble.

Among the thermally activable polymerization initiators preference isgiven to initiators having a decomposition temperature in the range from30 to 150° C., in particular from 50 to 120° C. This temperature figurerefers, as usual, to the 10 h half-life.

As initiators it is possible to use all of the compounds which breakdown into free radicals under the polymerization conditions, such as,for example, inorganic peroxo compounds, such as peroxodisulfates,especially ammonium peroxodisulfate, potassium peroxodisulfate andpreferably sodium peroxodisulfate, peroxosulfates, hydroperoxides,percarbonates, and hydrogen peroxide and what are called redoxinitiators. Preference is given to the use of water-soluble initiators.In certain cases it is advantageous to use mixtures of differentinitiators, examples being mixtures of hydrogen peroxide and sodium orpotassium peroxodisulfate. Mixtures of hydrogen peroxide and sodiumperoxodisulfate can be used in any desired proportion.

Suitable organic peroxo compounds are diacetyl peroxide, di-tert-butylperoxide, diamyl peroxide, dioctanoyl peroxide, didecanoyl peroxide,dilauroyl peroxide, dibenzoyl peroxide, bis(o-toluoyl) peroxide,succinyl peroxide, tert-butyl peracetate, tert-butyl permaleate,tert-butyl perisobutyrate, tert-butyl perpivalate, tert-butylperoctoate, tert-butyl perneodecanoate, tert-butyl perbenzoate,tert-butyl peroxide, tert-butyl hydroperoxide (water soluble), cumenehydroperoxide, tert-butyl peroxy-2-ethylhexanoate, and diisopropylperoxydicarbamate.

Preferred initiators are, moreover, azo compounds. These may be solublein organic solvents, as is the case, for example, for2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl2,2′-azobis(2-methylpropionate),1,1′-azobis(cyclohexane-1-carbonitrile),1-[(cyano-1-methylethyl)azo]formamide,2,2′-azobis(N-cyclohexyl-2-methylpropionamide),2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2-methylbutyronitrile),2,2′-azobis[N-(2-propenyl)-2-methylpropionamide],2,2′-azobis(N-butyl-2-methylpropionamide). Preferably, however, they aresoluble in water, as is the case for example for2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane] disulfate dihydrate,2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate,2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride,2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide,2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis(2-methylpropionamide) dihydrochloride,2,2′-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride, 2,2′-azobis[2-(2-imidazolin-2-yl)propane],2,2′-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamide}.

Additionally preferred initiators are, moreover, redox initiators. Theredox initiators comprise as oxidizing component at least one of theperoxo compounds indicated above and as reducing component, for example,ascorbic acid, glucose, sorbose, ammonium or alkali metal hydrogensulfite, sulfite, thiosulfate, hyposulfite, pyrosulfite or sulfide orsodium hydroxymethylsulfoxylate. As a reducing component in the redoxcatalyst it is preferred to use ascorbic acid or sodium pyrosulfite.Relative to the amount of monomers used in the polymerization the amountof reducing component used in the redox catalyst is, for example, 1×10⁻⁵to 1 mol %.

In combination with the initiators and/or the redox initiator systems itis possible in addition to use transition metal catalysts, examplesbeing salts of iron, cobalt, nickel, copper, vanadium, and manganese.Examples of suitable salts include iron(II) sulfate, cobalt(II)chloride, nickel(II) sulfate, and copper(I) chloride. The reductivetransition metal salt is usually used in an amount of from 0.1 to 1 000ppm, based on the sum of the monomers. Particularly advantageouscombinations are, for example, those of hydrogen peroxide and iron(II)salts, such as a combination of from 0.5% to 30% by weight of hydrogenperoxide and from 0.1 to 500 ppm of FeSO₄x7H₂O, based in each case onthe sum of the monomers.

Examples of suitable photoinitiators are acetophenone, benzoin ethers,benzyl dialkyl ketones, and derivatives thereof. They are insoluble orvirtually so in water but probably soluble in alcohols, so that adispersing can be achieved.

It is preferred to use thermal initiators, with preference being givento water-soluble azo compounds and water-soluble peroxo compounds.Particular preference is given to inorganic peroxo compounds, especiallyhydrogen peroxide and in particular sodium peroxodisulfate or mixturesthereof, optionally in combination with from 0.1 to 500 ppm ofFeSO₄x₇H₂O. Especial preference is given to hydrogen peroxide.

It will be appreciated that mixtures of different initiators can also beused subject to the proviso that they do not influence one anothernegatively. The amount is determined by the skilled worker in accordancewith the desired copolymer. As a general rule from 0.05% to 20%,preferably from 0.1% to 15%, and more preferably from 0.2% to 8% byweight is used of the initiator, relative to the total amount of allmonomers.

It is also possible, furthermore, in a manner which is known inprinciple, to use suitable regulators, such as mercaptoethanol, forexample. Preferably no regulators are used.

The polymerization may also be performed in the presence of a base. Bythis means the acidic groups, particularly the carboxyl groups of themonomers, are wholly or partly neutralized.

Bases which can be used include, for example, NaOH, KOH or NH₃. Aminesas well are suitable.

Examples of suitable amines comprise linear, cyclic and/or branchedC₁-C₈ mono-, di- and trialkylamines, linear or branched C₁-C₈ mono-, di-or trialkanolamines, especially mono-, di- or trialkanolamines, linearor branched C₁-C₈ alkyl ethers of linear or branched C₁-C₈ mono-, di- ortrialkanolamines, oligoamines and polyamines such as diethylenetriamineor polyethyleneimines, heterocyclic amines such as morpholine,piperazine, imidazole and piperidine, or else certain aromatic amines,such as benzotriazole or tolyltriazole, for example. The amines can alsobe alkoxylated, in particular ethoxylated. By this means it is possiblewith advantage to increase the water solubility of amines havingrelatively long alkyl chains.

The skilled worker makes an appropriate selection from among the amines.

Preference is given to linear or branched C₁-C₈ mono-, di- ortrialkanolamines, particular preference being given to mono-, di- andtriethanolamine and/or the corresponding ethoxylated products.

If bases are used the degree of neutralization should generally notexceed 30 mol %, based on the total amount of all of the acidic groupsof the monomers. Preferably the degree of neutralization is not morethan 20 mol %, more preferably not more than 10 mol %.

With very particular preference no base is used.

The bases can be added before or during the polymerization. Preferablyit is added before the polymerization or no later than at the beginningof the polymerization. The base can be added either all at once orwithin a time interval which corresponds at most to the entire reactionperiod. The base can be added to the monomer feed. Preferably the baseis included in the initial charge before the polymerization iscommenced.

In accordance with the invention the polymerization is performed at atemperature of less than 120° C. Apart from this the temperature can bevaried by the skilled worker within wide limits, in accordance with thenature of the monomers used, the initiator, and the desired result.Established in this context is a minimum temperature of approximately60° C. The temperature can be held constant during the polymerization orelse it is possible to operate temperature profiles. The polymerizationtemperature is preferably 75 to 115° C., more preferably 80 to 110° C.,with particularly preference 90 to 108° C., and very preferably 95 to105° C.

The polymerization can be performed in usual apparatus for free-radicaladdition polymerization. When operating above the boiling temperature ofthe water or of the mixture of water and further solvents operationtakes place in a suitable pressure vessel, while otherwise operation maytake place at atmospheric pressure. The polymerization is preferablyperformed at atmosphere pressure. Polymerization can be carried out, forexample, under reflux.

In connection with the polymerization it is generally proven appropriateto include itaconic acid and/or derivatives thereof in aqueous solutionin the initial charge. Thereafter it is possible to meter in themonocarboxylic acid and also the initiator, appropriately likewise inaqueous solution. Feed times which have proven appropriate are from 0.5h to 24 h, preferably 1 h to 12 h.

In this way the concentration of the more reactive monocarboxylic acidsin the aqueous solution is kept relatively low. This reduces thetendency of the monocarboxylic acid to react with itself and produces amore uniform incorporation of the itaconic acid units into thecopolymer. Where monomers (C) and/or (D) used optionally are slow toreact, it is likewise advisable to include them in the initial chargetogether with the itaconic acid. It will be appreciated, however, thatthey can also be added dropwise later. After all of the monomers havebeen fed in there may also be an afterreaction time, of from 0.5 to 3 h,for example. This ensures that the polymerization reaction proceeds asfar as possible to completion.

The skilled worker, of course, can also perform the polymerization inanother way.

The synthesized polymers can be isolated from the aqueous solution bymeans of customary methods known to the skilled worker: for example, byevaporating down the solution, by spray drying, by freeze drying or byprecipitation.

With particular preference, however, the polymers after thepolymerization are not isolated from the aqueous solution at all;instead, the resulting polymer solutions are used as they are.

In order to make such direct further use easier the amount of aqueoussolvent ought right from the start to be such that the concentration ofthe polymer in the solvent is suitable for the application. Aconcentration which has proved particularly appropriate is that from 15%to 70% by weight, relative to the sum of all of the components;preferably from 20% to 65% by weight, more preferably from 25% to 60% byweight, and, for example, from 45% to 55% by weight.

The polymers of the invention are soluble or at least dispersible inwater or in aqueous solvent mixtures with a water content of at least50% by weight, the skilled worker being aware that the solubility ofCOOH-rich polymers can be highly pH-dependent. Reference is thereforemade here to the pH values at which the polymers are used forpassivation, in other words to an acidic solution, in particular to thepH range from 0.5 to 6. The term “water-dispersible” means that,although the solution is not entirely clear, the polymer is neverthelesshomogeneously distributed therein and also does not settle. The polymersin question are preferably polymers which are water-soluble.

The pH of the polymer solution is generally less than 5, preferably lessthan 4, and more preferably less than 3.

The molecular weight M_(w) (weight average) of the copolymers is from5000 to 2 000 000 g/mol, preferably at least 10 000 g/mol, morepreferably at least 15 000 g/mol. In general M_(w) is from 20 000 g/molto 1 000 000 g/mol, preferably from 30 000 g/mol to 900 000 g/mol, morepreferably from 40 000 g/mol to 800 000 g/mol, and very preferably from50 000 g/mol to 700 000 g/mol. It is determined by the skilled worker inaccordance with the desired end use.

The preparation of the polymer or polymers that is used in accordancewith the invention is an aqueous acidic formulation.

The polymers of the invention can be used in particular for treatingmetallic surfaces. For this purpose the polymers of the invention can beused in particular as components of corresponding formulations: forexample, as components of cleaners, pickling solutions, corrosioncontrol compositions and/or formulations for passivating.

The copolymers of the invention can be used with particular advantagefor passivating metallic surfaces or for forming passivating layers onmetals. Instead of the term “passivating layer” the term “conversioncoat” is often used synonymously, and sometimes also the term“pretreatment layer”. The copolymers of the invention are particularlysuitable for chromium-free passivation.

Any metallic surfaces can be treated, and in particular passivated, bymeans of the polymers of the invention. Preferably, however, thesurfaces are those of low- or high-alloy steel or those of Zn, Znalloys, Al or Al alloys. These may be the surfaces of structures orworkpieces composed entirely of said metals and/or alloys. Alternativelythey may be the surfaces of structures coated with Zn, Zn alloys, Al orAl alloys, it being possible for the structures to be composed of othermaterials: for example, other metals, alloys, polymers or composites.The surface in question may in particular be that of galvanized iron orsteel. In one particular embodiment of the process it is the surface ofa strip metal, in particular electrolytically galvanized orhot-dip-galvanized steel. In a further-preferred embodiment the surfacein question may be that of an automobile body.

Zn alloys or Al alloys are known to the skilled worker. The skilledworker selects the type and amount of alloying constituents inaccordance with the desired end application. Typical constituents ofzinc alloys for hot-dip processes comprise, in particular, Al, Pb, Si,Mg, Sn, Cu or Cd. Typical alloying components in Zn alloys which aredeposited electrolytically are Ni, Fe, Co and Mn. Typical constituentsof aluminum alloys comprise, in particular, Mg, Mn, Si, Zn, Cr, Zr, Cuor Ti.

The alloys in question can also be Al/Zn alloys in which Al and Zn arepresent in approximately equal amounts. Steel coated with such alloys isavailable commercially.

The solvent or diluent used for the copolymers is water or an aqueoussolvent mixture comprising at least 50% by weight of water. If anaqueous mixture is employed the mixture preferably comprises at least65% by weight, more preferably at least 80% by weight and verypreferably at least 95% by weight, of water. The amounts are based ineach case on the total amount of all solvents. Further components of amixture may be water-miscible solvents. Examples comprise monoalcoholssuch as methanol, ethanol or propanol, higher alcohols such as ethyleneglycol or polyether polyols, and ether alcohols such as butyl glycol ormethoxypropanol.

Preferably only water is used as solvent.

The concentration of the copolymers in the preparation is determined bythe skilled worker in accordance with the desired end application. Thethickness of the passivating layer depends, for example, on the chosenprocess technology, but may also depend on the viscosity of thecomposition used for passivating. Generally speaking a concentrationwhich has proven appropriate is that from 0.01 g/l to 500 g/l,preferably from 0.1 g/l to 200 g/l and more preferably from 0.5 g/l to 5g/l. The stated concentrations are based on the preparation inready-to-use form. Generally it is possible first to prepare aconcentrate, which only in situ is diluted to the desired concentrationusing water or, optionally, other solvent mixtures.

The preparation used in accordance with the invention is acidic. Itgenerally has a pH of from 0.5 to 6, with the choice of narrower pHranges being possible in accordance with the substrate and mode ofapplication and also with the time during which the surface is exposedto the preparation. By way of example the pH is adjusted preferably tothe range from 2 to 4 for the purpose of treating aluminum surfaces andto the range from 1 to 5 in the case where zinc or galvanized steel isbeing treated.

The pH of the preparation may be controlled on the one hand through thenature and concentration of the COOH-containing polymers or copolymersand, accordingly, comes about automatically. In this context it shouldbe borne in mind that as a result of preparation the COOH groups in thepolymer may in certain circumstances have been fully or partlyneutralized.

As an alternative option the preparation may further comprise at leastone organic or inorganic acid or mixtures thereof. Examples of suitableacids comprise phosphorus, sulfur or nitrogen acids such as phosphoricacid, phosphonic acid, sulfuric acid, sulfonic acids such asmethanesulfonic acid, amidosulfonic acid, p-toluenesulfonic acid,m-nitrobenzenesulfonic acid, and derivatives thereof, nitric acid,hydrofluoric acid, hydrochloric acid, formic acid or acetic acid. Theacid is preferably selected from the group consisting of HNO₃, H₂SO₄,H₃PO₄, formic acid and acetic acid. Particular preference is given toH₃PO₄ and/or HNO₃. It will be appreciated that mixtures of differentacids can also be used.

Conversely, bases may also be used to increase the pH, if appropriate.

Examples of phosphonic acids comprise 1-hydroxyethane-1,1-diphosphonicacid (HEDP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC),aminotri(methylenephosphonic acid) (ATMP),ethylenediaminetetra(methylenephosphonic acid) (EDTMP) ordiethylenetriaminepenta(methylenephosphonic acid) (DTPMP).

The nature and concentration of the acid in the preparation isdetermined by the skilled worker in accordance with the desired endapplication and pH. Generally speaking, a concentration which has provenappropriate is that from 0.01 g/l to 30 g/l, preferably from 0.05 g/l to3 g/l and more preferably from 0.1 g/l to 5 g/l.

The preparation may also comprise, optionally, further components beyondthose specified.

The components present optionally may be, for example, transition metalions and transition metal compounds, examples being those of Ce, Ni, Co,V, Fe, Zn, Zr, Ca, Mn, Mo, W, Ti, Zr, Hf, Bi, Cr and/or of thelanthanides. They may also be compounds of main group elements, such asSi and/or Al, for example. The compounds can be used for example in theform of the respective aqua complexes. They may also, however, becomplexes with other ligands, such as fluoride complexes of Ti(IV),Zr(IV) or Si(IV), or oxometallates such as MoO₄ ²⁻ or WO₄ ²⁻, forexample. It is also possible, moreover, to use complexes with typicalchelate-forming ligands such as ethylenediaminetetraacetic acid (EDTA),diethylenetriaminepentaacetic acid (DTPA),hydroxyethylethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid(NTA) or methylglycinediacetic acid (MGDA).

Further optional components comprise surface-active compounds, corrosioninhibitors or typical electroplating auxiliaries. The skilled workermakes an appropriate selection from among the optional components thatare possible in principle, with respect also to their amounts, inaccordance with the desired application. Examples of particularlypreferred corrosion inhibitors which can be used in combination with theitaconic acid polymers comprise benzotriazole and/or tolyltriazole.

For the purpose of fine tuning its properties the formulation may alsocomprise further water-soluble polymers as additional components.Examples of such polymers comprise in particular polymers comprisingcarboxylate groups which merely do not correspond to the abovedefinition of the composition. Examples that may be mentioned includepoly(meth)acrylic acids and also copolymers of (meth)acrylic acid withother monomers containing acid groups, such as maleic acid, fumaricacid, crotonic or vinylacetic acid, for example. The amount of suchadditional (co)polymers is determined by the skilled worker inaccordance with the desired properties of the passivating layer. Theamount in general, however, should not exceed 30% by weight, preferably20% by weight and more preferably 10% by weight, based on the amount ofall the polymers used.

The passivation in question is preferably a substantially chromium-freepassivation. This is intended to denote that small amounts, at best, ofchromium compounds could be added in order to fine-tune the propertiesof the passivating layer. The amount should not exceed 2%, preferably 1%and more preferably 0.5% by weight of chromium, based on allconstituents of the composition. If chromium compounds are to beemployed then it is preferably Cr(III) compounds that should beemployed. In each case, however, the Cr(VI) content should be kept solow that the amount of Cr(VI) on the passivated metal does not exceed 1mg/m².

With particular preference the passivation is a chromium-freepassivation; in other words, the preparation employed contains no Crcompounds at all. The expression “chromium-free”, however, does not ruleout the indirect and per se unintended entrainment of small amounts ofchromium into the process. Indeed, if the process of the invention isused to passivate alloys which comprise chromium as an alloyingconstituent, Cr-containing steel for example, it is always within thebounds of possibility for small amounts of chromium in the metal to betreated to be dissolved by the preparation used for the process and,accordingly, to pass into the preparation unintentionally per se. Evenin the case where such metals are used, with the resultant consequences,the process should still be regarded as “chromium-free”.

In the process of the invention for passivating metallic surfaces thesurface of the metal is treated with the preparation by means, forexample, of spraying, dipping or rolling. After a dipping operationexcess treatment solution can be removed from the workpiece by allowingit to drip dry; in the case of metal sheets, metal foils or the likeexcess treatment solution can alternatively be removed by squeezing offor squeegeeing, for example. In the course of the treatment parts atleast of the polymer used and also further components of the preparationare chemisorbed by the surface of the metal, so that a solid bond comesabout between the surface and the component. Treatment with thepreparation takes place generally at room temperature or above, althoughthis is not intended to rule out the possibility of lower temperaturesin principle. As a general rule the treatment takes place at from 20 to90° C., preferably from 25 to 80° C. and more preferably from 30 to 60°C. For that purpose the bath containing the formulation can be heated,although an elevated temperature may also come about automatically, bythe immersion of hot metal into the bath.

It is possible to rinse the surface, after treatment, with a cleaningliquid, in particular with water, in order to remove residues of thepreparation used in accordance with the invention from the surface.

The treatment may alternatively be what is called a no-rinse operation,in which the treatment solution is dried directly in a drying ovenimmediately following its application, without rinsing.

The treatment of the metal surface with the preparation and thecrosslinker can take place discontinuously or, in particular,continuously. A continuous process is particularly suitable for treatingstrip metals. The metal strip is run through a trough or a sprayingapparatus with the preparation and also, optionally, through a trough orspraying apparatus, and also, optionally, through further pretreatmentor aftertreatment stations.

The treatment time is specified by the skilled worker in accordance withthe desired properties of the layer, the composition used for thetreatment, and the technical boundary conditions. It may be considerablyless than one second or may be two or more minutes. In the case of thecontinuous process it has proven particularly appropriate to contact thesurface with the preparation for a time of from 1 to 60 s.

Following the treatment the solvent used is removed. It can be removedat room temperature by simple evaporation in air at room temperature.

Alternatively the removal of the solvent may be assisted by means ofsuitable auxiliaries, such as by heating and/or passing streams of gas,particularly streams of air, over the treated surface. The evaporationof the solvent can be assisted, for example, by means of IR emitters, orelse, for example, by drying in a drying tunnel. For the purpose ofdrying a temperature which has proven appropriate is that from 30° C. to160° C., preferably from 40° C. to 100° C. and more preferably from 50°C. to 80° C. This refers to the temperature on the metal surface; it maybe necessary to set the dryer temperature at a higher level, which ischosen appropriately by the skilled worker.

The process of the invention may optionally comprise one or morepretreatment steps. For example, prior to passivation, the metallicsurface can be cleaned with the preparation used in accordance with theinvention, in order for example to remove greases or oils. It is alsopossible to pickle the surface prior to passivation, in order to removeoxide deposits, scale, temporary corrosion protection, and the like. Itis additionally necessary to rinse the surface, with water ifappropriate, after and between such pretreatment steps, and to removethe residues of rinsing solutions or pickling solutions.

The passivating layer may additionally be crosslinked. For this purposeit is possible, for example, to admix a crosslinker to the preparationused, provided said crosslinker does not react while still in thepreparation. An alternative is first to treat the metal with thepreparation and thereafter to treat the layer with a suitablecrosslinker for example, to spray it with a solution of a crosslinker.

Suitable crosslinkers should be water-soluble or at least soluble in theaforementioned aqueous solvent mixture. Examples of suitablecrosslinkers comprise in particular those which have at least twocrosslinking groups selected from the group of azirane groups, oxiranegroups or thiirane groups. Further details of suitable crosslinkers aredisclosed in our application WO 2005/042801, hereby expresslyincorporated by reference.

The process of the invention makes it possible to obtain a passivatinglayer on a metallic surface. The precise structure and composition ofthe passivating layer are unknown to us. However, in addition to thecustomary amorphous oxides of aluminum or of zinc and also, ifappropriate, of other metals, said layer comprises the reaction productsof the polymer and also, where appropriate, of the crosslinker and/or offurther components of the formulation. The composition of thepassivating layer is generally not homogeneous; rather, the componentsappear to exhibit concentration gradients.

The thickness of the passivating layer is adjusted by the skilled workerin accordance with the desired properties of the layer. In general thethickness is from 0.01 to 3 μm, preferably from 0.1 to 2.5 μm, morepreferably from 0.2 to 2 μm, most preferably from 0.3 to 1.5 μm, and forexample from 1 to 2 μm. The thickness can be influenced, for example, byway of the nature and amount of the components applied, and also by wayof the exposure time. In addition, it is possible to use technicalparameters of the process to influence the thickness: by using rollersor squeegees to remove treatment solution applied in excess, forexample.

The thickness of the layer is determined by differential weighing beforeand after exposure of the metal surface to the composition used inaccordance with the invention, on the assumption that the layer has aspecific density of 1 kg/l. In the text below, “layer thickness” alwaysrefers to a variable determined in this way, irrespective of the actualspecific density of the layer. These thin layers are enough to obtainoutstanding corrosion protection. Thin layers of this kind ensure thatthe dimensions of the passivated workpieces are maintained.

The present specification further provides a metallic surface whichcomprises the passivating layer of the invention. The passivating layeris applied directly on the actual metal surface. In one preferredembodiment the metal surface in question is that of a strip metal ofsteel which comprises a coating of Zn or of Zn alloy and on which apassivating layer of the invention has been applied. The surface inquestion may also be that of an automobile body which has been coatedwith the passivating layer of the invention.

The metallic surface with its passivating layer may in principle beovercoated in a known manner with one or more color or effect paintlayers. Typical paints, their composition, and typical layer sequencesin the case of two or more paint layers are known in principle to theskilled worker.

The passivation of the invention can be employed at different processingstages. It can be undertaken, for example, at the premises of a steelmaker. In this case a steel strip can be galvanized in a continuousprocess and immediately after having been galvanized can be passivatedby treatment with the formulation used in accordance with the invention.Passivation at this stage is frequently referred to by the skilledworker as “aftertreatment”.

The passivation in question may be only temporary, serving to protectagainst corrosion in the course of storage and transport and/or duringfurther process steps, but removed again before the permanent corrosionprotection is applied. The acidic copolymers can be removed from thesurface again by cleaning with aqueous alkaline solutions.

Alternatively the treatment may be a permanent corrosion protectiontreatment, which remains on the strip or on the fully-formed workpieceand is provided with additional paint coats. Passivation at this stageis frequently referred to by the skilled worker as “pretreatment”.

The passivated and, if appropriate, painted metal sheets, strips orother semifinished metallic products can be processed further to formmetallic workpieces, such as an automobile body, for example. Thisgenerally necessitates at least one separating step and one formingstep. Larger components can be assembled subsequently from individualcomponents. Forming involves changing the shape of the material,generally in contact with a tool. Forming may, for example, involvecompressive forming, such as rolling or embossing, tensile compressiveforming, such as cold drawing, deep drawing, roll-bending orpress-bending, tensile forming such as lengthening or widening, flexuralforming such as bending, edge-rolling or edging, and shearing formingsuch as twisting or dislocating.

The process of the invention for passivating achieves much bettercorrosion protection than when using itaconic acid copolymers which havebeen obtained at relatively high temperatures.

The examples which follow are intended to illustrate the invention inmore detail:

Measurement Methods:

The K values were measured by the method of H. Fikentscher,Cellulose-Chemie, vol. 13, pp. 58-64 and 71-74 (1932) in 1% strength byweight aqueous solution at 25° C. M_(w) values were determined by meansof gel permeation chromatography.

Preparation of the Polymers COMPARATIVE EXAMPLE 1

Copolymer of 75% by weight acrylic acid and 25% by weight maleic acid

A 6 l pressure reactor with anchor stirrer, temperature monitoring andnitrogen inlet is charged with 480 g of maleic anhydride and 22.5 mg ofiron sulfate in one liter of deionized water.

This initial charge is heated at 115 to 120° C. under a nitrogenatmosphere. When this temperature has been reached 1670 g of acrylicacid in 1.2 l of deionized water are metered in at a uniform rate overthe course of 4 h and 115 g of 30% strength hydrogen peroxide solutionand 300 ml of deionized water are metered in at a uniform rate over thecourse of 5 h. During the polymerization the pressure is maintained atfrom 3 to 4 bar by careful release of pressure.

Cooling gives a yellowish, clear polymer solution having a solidscontent of 45.6% and a K value (1% in deionized water) of 26.0.

COMPARATIVE EXAMPLE 2

Copolymer of acrylic acid/itaconic acid (73/27), polymerization at 120°C. in a pressure reactor

A 6 l pressure reactor provided with anchor stirrer, temperaturemonitoring, nitrogen inlet and 2 feed ports is charged with 444 g ofitaconic acid, 15.5 mg of iron sulfate heptahydrate and 889 g ofdeionized water.

This initial charge is heated to 120° C. under a nitrogen atmosphere.When this temperature has been reached feed stream 1, consisting of1188.0 g of acrylic acid and 926 g of deionized water, is metered in ata uniform rate over the course of 5 h and also feed stream 2, consistingof 81.6 g of hydrogen peroxide (30% strength) and 177 g of deionizedwater, is metered in at a uniform rate over the course of 6 hours. Afterthe end of feed stream 1 a further 133 g of deionized water are added.The reaction mixture is stirred at 120° C. for a further 2 hours. Duringthe polymerization the pressure is held at from 3 to 4 bar by carefulrelease of pressure. The batch is diluted with water.

Cooling gives a yellowish, clear polymer solution having a solidscontent of 17.9% and a K value (1% strength in deionized water) of 83.5.No free itaconic acid was detectable by means of the ¹H NMR spectrum.

EXAMPLE 1 Copolymer of Acrylic Acid and Itaconic Acid (73/27),Unpressurized Polymerization at 100° C.

In a stirring pot with blade stirrer and internal thermometer 111.0 g ofitaconic acid are dissolved with 250 g of deionized water and, followingthe addition of 3.875 mg of iron(II) sulfate heptahydrate, the solutionis heated at slight reflux (internal temperature: 98° C.). Subsequently,over the course of 5 h, feed stream 1, consisting of 297.0 g of acrylicacid and 398.0 g of deionized water, and, over the course of 6 h, feedstream 2, consisting of 6.12 g of sodium peroxodisulfate in 180 g ofwater, are added. After the end of feed stream 1 the system is stirredat 98° C. for further 2. This gives a pale yellow, clear polymersolution having a solids content of 36.4% and a K value (1% strength indeionized water) of 59.6. No free itaconic acid was detectable by meansof the ¹H NMR spectrum.

EXAMPLE 2 Copolymer of Acrylic Acid and Itaconic Acid (73/27);Unpressurized Polymerization at 100° C.

In a stirring pot with blade stirrer and internal thermometer 111.0 g ofitaconic acid are dissolved with 250 g of deionized water and, followingthe addition of 3.875 mg of iron(II) sulfate heptahydrate, the solutionis heated at slight reflux (internal temperature: 98° C.). Subsequently,over the course of 5 h, feed stream 1, consisting of 297.0 g of acrylicacid and 398.0 g of deionized water, and, over the course of 6 h, feedstream 2, consisting of 20.4 g of hydrogen peroxide (30% strength) in180 g of water, are added. After the end of feed stream 1 the system isstirred at 98° C. for further 2. The batch is diluted in a number ofportions with a total of 750 g of water. This gives a pale yellow, clearpolymer solution having a solids content of 15.0% and a K value (1%strength in deionized water) of 115.2. No free itaconic acid wasdetectable by means of the ¹H NMR spectrum.

EXAMPLE 3 Terpolymer of Acrylic Acid, Itaconic Acid and VinylphosphonicAcid (69/26/5); Unpressurized Polymerization at 100° C.

In a stirring pot with blade stirrer and internal thermometer 111.0 g ofitaconic acid are dissolved with 250 g of deionized water and, followingthe addition of 3.875 mg of iron(II) sulfate heptahydrate, the solutionis heated at slight reflux (internal temperature: 98° C.). Subsequently,over the course of 5 h, feed stream 1, consisting of 297.0 g of acrylicacid, 22.7 g of vinylphosphonic acid and 346.0 g of deionized water,and, over the course of 6 h, feed stream 2, consisting of 42.8 g ofhydrogen peroxide in 180 g of water, are added. After the end of feedstream 1 the system is stirred at 98° C. for further 2. The batch isdiluted in a number of portions with a total of 700 g of water. Thisgives a pale yellow, clear polymer solution having a solids content of21.2% and a K value (1% strength in deionized water) of 37.8.

EXAMPLE 4 Copolymer of Acrylic Acid, Itaconic Acid and Vinyl PhosphonicAcid

In a stirring pot with blade stirrer and internal thermometer 161.3 g ofitaconic acid and 152 of vinylphosphonic acid (95%) are dissolved with200 g of deionized water and, following the addition of 703 mg ofiron(II) sulfate heptahydrate, the solution is heated at slight reflux(internal temperature: 98° C.). Subsequently, over the course of 5 h,feed stream 1, consisting of 430.0 g of acrylic acid and 455 g ofdeionized water, and, over the course of 6 h, feed stream 2, consistingof 42.5 g of sodium peroxodisulfate in 160 g of water, are added. Afterthe end of feed stream 1 the system is stirred at 98° C. for further 2h. This gives a pale yellow, clear polymer solution having a solidscontent of 48.8% and a K value (1% strength in deionized water) of 28.2.

Passivation of Metallic Surfaces Metallic Surface and its Pretreatment:

The tests were carried out using in each case alkalinically galvanizedor hot-dip-galvanized steel sheets (approx. 100×190×0.7 mm; 20 μm zincadd-on).

The alkalinically galvanized steel sheets (AV) are immersed in acleaning solution (0.5% HCl+0.1% Lutensol® AP 10, BASF AG) for about 5seconds and immediately rinsed with deionized water and dried byblowing.

The hot-dip-galvanized steel sheets (HV) are immersed in an alkalinedegreaser at 50° C. for 120 seconds and immediately rinsed withdeionized water and dried by blowing.

Employment of the Preparation Used in Accordance with the Invention

The synthesized polymers were dissolved in water (solids content 5% byweight), homogenized and introduced into a dip bath. The cleaned metalsheets are immersed directly for 30 s in the polymer solution, which hasbeen conditioned to a temperature of 50° C., and are dried at RT. Theedges of the passivated sheet are masked off.

Differential Weighing

The thickness of the layer is determined by differential weighing beforeand after the metal surface has been exposed to the compositionemployed, on the assumption that the layer has a specific density of 1kg/l. In the text below “layer thickness” always refers to a parameterdetermined in this way, irrespective of the actual specific density ofthe layer.

The layer thicknesses determined by differential weighing are between1.5 and 3 μm. The withstand time is determined in a salt spray misttest.

Test Method Salt Spray Test

The result of a salt spray test in accordance with DIN 50021 is used asa measure of the corrosion inhibition effect. The withstand time in thecorrosion test is defined differently according to what kind ofcorrosion damage is observed.

-   -   if white spots of generally more than 1 mm in diameter (Zn oxide        or Al oxide, known as white rust) are formed, the withstand time        reported is the time after which the appearance of the damage        corresponds to evaluation level 8 in DIN EN ISO 10289 of April        2001, annex B, page 19.    -   if black spots of generally less than 1 mm in diameter form        before white rust spots (particularly on zinc provided with a        passivating layer), the withstand time reported is the time        after which the appearance of the damage corresponds to        evaluation level 8 in DIN EN ISO 10289 of April 2001, annex A,        page 9.        Test chamber volume: 400 l        Spray mist throughput measured according to DIN: 2.2 ml/h

The results of the tests are assembled in table 1.

TABLE 1 Results of the inventive and comparative examples Polymeri-Residual Withstand time [h] zation Initiator/ mono. alkalin- AcrylicItaconic Further temperature Pressure amount Fe dicarboxylic M_(w)ically hot-dip- Example acid acid comonomers [° C.] [bar] [wt. %] [ppm]K value acid [g/mol] galvanized galvanized Comparative 75 — 25% maleic 120° 3-4 H₂O₂/ 2 26 4.5%  85 000 30 18 example 1 acid 1.5 Comparative73 27 — 120 3-4 H₂O₂/ 2 83.5 not 304 000 35 20 example 2 1.5 detectablein the ¹H NMR Inventive 73 27 — 100 1 NaPS/ 2 59.6 not 630 000 52 23example 1 1.5 detectable in the ¹H NMR Inventive 73 27 — 100 1 H₂O₂/ 2115.2 not 510 000 50 28 example 2 1.5 detectable in the ¹H NMR Inventive69 26 5% 100 1 H₂O₂/ 2 37.8 n.d. 610 000 51 35 example 3 vinylphos- 3.0phonic acid Inventive 58 22 20% 100 1 NaPS/ 250 28.2 n.d. n.d. — 55Example 4 vinylphos- 3.6 phonic acid n.d. not determined

The inventive and comparative examples show that by means of the processof the invention for passivating using itaconic acid polymers with apolymerization temperature of less than 120° C. a much better corrosionprotection is achieved than when using itaconic acid polymers which havebeen prepared by polymerization at higher temperatures. The efficacy isalso higher than that of acrylic acid-maleic acid copolymers.

1-20. (canceled)
 21. A process for passivating a metallic surface bytreating it with an acidic aqueous preparation comprising at least onewater-soluble or water-dispersible itaconic acid copolymer, wherein thecopolymer has been constructed from the following monomeric units: (A)15% to 45% by weight of itaconic acid, (B) 55% to 85% by weight of atleast one monoethylenically unsaturated monocarboxylic acid, (C) 5% to40% by weight of vinylphosphonic acid, and (D) optionally 0% to 30% byweight of at least one further ethylenically unsaturated monomer, otherthan (A), (B) and (C), the amount being based in each case on the totalamount of all of the monomers incorporated in the copolymer, and thecopolymer being obtainable by means of free-radical polymerization inaqueous solution at a temperature of less than 120° C.
 22. The processaccording to claim 21, wherein the amount of vinylphosphonic acid is 10%to 30% by weight.
 23. The process according to claim 21, wherein thepolymer is a terpolymer of 67% to 75% acrylic acid, 23% to 30% itaconicacid, and 0.1% to 10% vinylphosphonic acid, by weight.
 24. The processaccording to claim 21, wherein the polymer is a terpolymer of 55% to 65%acrylic acid, 15% to 25% itaconic acid, and 15% to 25% vinylphosphonicacid, by weight.
 25. The process according to claim 21, wherein thepolymerization is performed at a temperature from 90 to 105° C.
 26. Theprocess according to claim 21, wherein said metallic surface is of Zn,Al or alloys thereof.
 27. The process according to claim 21, being asubstantially chromium-free process.
 28. The process according to claim21, wherein the treating takes place by means of rolling, spraying ordipping methods.
 29. The process according to claim 21, wherein themetal surface is the surface of a strip metal.
 30. The process accordingto claim 29, wherein the strip metal is electrolytically galvanized orhot-dip-galvanized steel.
 31. The process according to claim 29, whereinthe treating is performed by means of a continuous process.
 32. Theprocess according to claim 29, wherein the surface is contacted with thepreparation for a time of from 1 to 60 s.
 33. The process according toclaim 21, wherein the formulation further comprises benzo- and/ortolyltriazole.
 34. A water-soluble or water-dispersible itaconic acidcopolymer constructed from the following monomeric units: (A) 15% to 45%by weight of itaconic acid, (B) 55% to 85% by weight of at least onemonoethylenically unsaturated monocarboxylic acid, (C) 5% to 40% byweight of vinylphosphonic acid, and (D) optionally 0% to 30% by weightof at least one further ethylenically unsaturated monomer, other than(A), (B) and (C), the amount being based in each case on the totalamount of all of the monomers incorporated in the copolymer, and thecopolymer being obtainable by means of free-radical polymerization inaqueous solution at a temperature of less than 120° C.
 35. The copolymeraccording to claim 34, wherein the amount of vinylphosphonic acid is 10%to 30% by weight.
 36. The copolymer according to claim 34, wherein thepolymer is a terpolymer of 67% to 75% acrylic acid, 23% to 30% itaconicacid, and 0.1% to 10% vinylphosphonic acid, by weight.
 37. The copolymeraccording to claim 34, wherein the polymer is a terpolymer of 55% to 65%acrylic acid, 15% to 25% itaconic acid, and 15% to 25% vinylphosphonicacid, by weight.
 38. The copolymer according to claim 34, wherein thepolymerization is performed at a temperature from 90 to 105° C.